Typical processing of an integrated circuit produces an encapsulated package within which an IC die is supported by a die pad, with bond wires connected from bond pads disposed on the die to respective leads that extend externally from the encapsulated package. A generally planar, metal strip with patterned openings is used as a lead frame upon which several IC packages will be fabricated and thereafter separated from the lead frame. FIG. 1 is a perspective view of a portion of a typical lead frame 10 for one IC package prior to formation of the package. The dashed line block 12 circumscribes a portion of the metal strip that will be part of the package after completion of the process, including a die pad 14 and individual leads 16. The die pad is shown attached to the periphery of the lead frame by tie bars 20, which contain notches 22. The IC package is fabricated by adhesively mounting a die to the die pad, forming bonding connections between individual bond pads on the die and respective leads 16, and applying a molding compound to encapsulate the die pad, bond wires and leads substantially within the area defined by block 12. Thereafter, leads are detached from the common connection with the lead frame and further processed to obtain desired lead configurations. At this stage, the encapsulated package remains attached to the lead frame periphery by tie bars 20.
With standard methodology, separation of the encapsulated semiconductor package from the lead frame, commonly termed “singulation,” is achieved using tools that apply load directly to the package. The lead frame periphery is clamped and forced to separate from the package by thrust of a punch. The punch tends to force the package out of the plane of the supporting members, thus placing the connecting tie bar metal in tension. The deformed metal reaches its ultimate strength until a break occurs at notches 22. The forces applied to the package create a moment directly related to the application of the force. This moment can be devastating to the molded unit, resulting in silicon die cracking and/or plastic package cracking.
An additional problem encountered with conventional singulation techniques is the formation of “flash.” Flash is the result of the plastic molding operation. Due to tooling tolerances, the lead frame must maintain a distance from the edge of the molded unit to the singulation paring line. Flash is the plastic material that is trapped around the separation area of the lead frame. Plastic molding material protrudes from the package ends with varying degrees of distance. The presence of flash raises concerns that must be addressed in the methods of delivery of IC packages. Typical delivery methods include “tape and reel” delivery and “tube” delivery. With tape and reel delivery, units are placed into a pocket which is then sealed by tape. The size of the pocket must be chosen to accommodate all molded unit packages. Since flash tends to vary in a random fashion, large pockets must be provided. A tube delivery system transports a plurality of IC packages in each tube. A “shingling” problem often occurs as a result of flash interaction between adjoining packages, wherein the units are wedged in place within the tube. Safe and expedient removal of the packages from the tube becomes a difficulty.
The need thus exists for a singulation method and apparatus that avoid damaging the semiconductor packages, eliminate flash, and for an improved lead frame configuration that is compatible with such method and apparatus.